1. Field of the Invention
The present invention generally relates to a control apparatus for a synchromesh type automatic transmission for an internal combustion engine of a motor vehicle. More particularly, the present invention is concerned with a technique for suppressing or mitigating a rapid or steep change of engine speed, e.g. rapid deceleration which may occur when an electromagnetic clutch is released upon starting of up-shift gear change operation.
2. Description of Related Art
As one of the methods of controlling the automatic transmission of synchromesh type, there may be mentioned a technique disclosed in Japanese Unexamined Patent Application Publication No. 35633/1985 (JP-A-60-35633). According to this control method, the clutch-releasing rate or speed (also referred as the clutch-off speed) and the throttle valve closing rate or speed are changed upon starting of the gear shift (speed change) operation in dependence on the depression stroke or position of an accelerator pedal which thus serves as a control parameter.
In the conventional control of the synchromesh type automatic transmission in which the depression stroke of the accelerator pedal is employed as the control parameter as mentioned above, there arises problems mentioned below. In general, correlation between the closing operation of the clutch and that of the throttle valve is not to be satisfactory. More specifically, when the accelerator pedal is manipulated during a period in which the throttle valve is controlled in the closing direction after the gear shift operation (speed change operation) has been started, there may arise such situation that the clutch remains yet to be opened (released) notwithstanding the throttle valve has reached the closed position or the clutch assumes the released (off) position before the throttle valve has reached the closed position, as a result of which rapid deceleration of the engine and hence the motor vehicle and/or a so-called engine blowup event may take place, giving rise to the problem.
In the light of the state of the art described above, it is an object of the present invention to provide a control apparatus for a synchromesh type automatic transmission which apparatus is capable of preventing or suppressing occurrence of raid deceleration of the engine, the engine blowup event or the like problem even when the accelerator pedal is manipulated in the course of the throttle valve being closed. To this end, the present invention teaches that when upshift operation is decided, a time point for starting the clutch releasing (clutch-off) operation is determined on the basis of a throttle valve closing speed which in turn is determined on the basis of the throttle opening degree at the time point for starting the upshift operation and the time taken for the clutch to be released or opened which time in turn is determined on the basis of a clutch exciting current and the engine rotation speed at the above-mentioned time point.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a general aspect of the present invention a control apparatus for a synchromesh type automatic transmission for automatically changing over a plurality of speed gear stages from one to another in an internal combustion engine, which apparatus includes an electromagnetic clutch capable of assuming alternatively a torque transmitting state and a torque interrupting state in response to a change of an exciting current fed to the electromagnetic clutch, an accelerator pedal position sensor for detecting a depression stroke of an accelerator pedal, an engine rotation speed sensor for detecting a rotation speed (rpm) of the engine, an electronically controlled throttle valve for adjusting an intake air quantity of the engine on the basis of an output signal of the accelerator pedal position sensor, and a control unit receiving as inputs thereto output signals of the accelerator pedal position sensor and the engine rotation speed sensor, respectively, wherein the control unit is arranged such that upon decision of start of upshift operation, the control unit controls a closing rate or speed of the electronically controlled throttle valve on the basis of the output signal generated by the accelerator pedal position sensor at a time point when the start of upshift operation is decided, so that the electronically controlled throttle valve assumes a fully closed position when the electromagnetic clutch assumes an open (off) position.
With the arrangement of the synchromesh type automatic transmission described above, the time point for starting the clutch releasing (clutch-off) operation can be determined on the basis of the throttle valve closing rate or speed which in turn is determined on the basis of the throttle opening degree at the time point for starting the upshift operation and the time taken for the clutch to be released or opened which time in turn is determined on the basis of a clutch exciting current and the engine rotation speed at the above-mentioned time point. By virtue of this arrangement, rapid deceleration of the engine, the engine blowup event or the like problem which the conventional synchromesh type automatic transmission suffers due to unsatisfactory relation between the clutch-on position and the throttle-closed position can effectively be suppressed.
In a preferred mode for carrying out the invention, the control unit may be so designed as to estimate a time taken for the electronically controlled throttle valve to reach the fully closed position on the basis of the closing rate or speed of the electronically controlled throttle valve and the throttle opening degree thereof at the time point when the upshift operation is started.
With the arrangement of the synchromesh type automatic transmission described above, degradation of comfortableness of the speed change operation due to occurrence of rapid deceleration can positively be prevented.
In another mode for carrying out the invention, the control unit may preferably be so designed as to arithmetically determine a time taken for the electromagnetic clutch to assume the open (off) state on the basis of a preset value of the exciting current at a time point when the clutch releasing operation is started on one hand and the engine rotation speed on the other hand.
With the arrangement of the synchromesh type automatic transmission described above, degradation of comfortableness of the speed change operation due to occurrence of rapid deceleration of the engine and the so-called engine blowup phenomenon can satisfactorily be prevented.
In still another mode for carrying out the invention, the control unit may preferably be so designed as to arithmetically determine the time point at which the clutch releasing operation is started on the basis of a difference between the time taken for the electronically controlled throttle valve to assume the fully closed position and the time taken for the electromagnetic clutch to be released.
With the arrangement of the synchromesh type automatic transmission described above, degradation of comfortableness of the speed change operation due to occurrence of the rapid deceleration of the engine and the so-called engine blowup phenomenon can be prevented with enhanced reliability.